This invention relates to a method of manufacturing a tunnel or shaft lining or pipeline of segments each of which is adapted to be connected to further segments.
For brevity the remainder of this specification will refer in general to tunnel linings, but this should in all situations be taken also to include shaft linings and the like. Where appropriate pipelines will also be discussed.
It is well known to manufacture of tunnel linings using curved segments connected end to end and side to side. In addition the manufacture of pipe linings from segments connected end to end is also well known. Such segments typically are formed from concrete with internal reinforcement of steel bars. However, there are disadvantages with such internally reinforced segments both in terms of the gradual degradation of the steel reinforcement and in terms of sealing the segments in fluid tight fashion to one another. This latter disadvantage is largely as a result of the nature of the concrete surfaces against which such seals press, which commonly have many irregularities.
Japanese patent specification JP01-154996 there is disclosed a method of making a curved lining segment in which a concrete core is lined externally with fibre reinforced cement mouldings. Each of a pair of mouldings is of a generally tray shaped configuration having a base and outstanding sides. The mouldings are arranged with the outstanding sides of the two trays facing one another. Concrete is then introduced into a substantially closed cavity thus produced, to form the segment.
Such a construction may simplify the manufacturing process, but it is necessary for the core to be provided with reinforcement as the cement mouldings will not provide substantial structural strength to the core.
First, this is because of the nature of cement mouldings. Cement, like concrete is not strong in tension, which is why it is essential to provide concrete with some reinforcement which is strong in tension.
Second, if such internal reinforcement was not included in the construction described in the earlier Japanese patent specification, it would be necessary for the edge portions, or at least a pair of the edge portions of the concrete core, to be reinforced to give the segment tensile strength. In the Japanese construction though, the outstanding sides of the two trays meet along the edge portions of the concrete body, so that regardless of the material from which the cement mouldings may alternatively be made, the mouldings cannot give any substantial reinforcement to the segment where such reinforcement is primarily needed.